Objective Findings on the associations between sex hormones and immune function are scarce and mixed, especially in women. To contribute to the understanding on how sex hormones and immune function interact, we analyzed relationships between testosterone, estradiol, and immune responses in women.

Methods Two doses of hepatitis B vaccine were administered to a group of 55 healthy women. Venous blood samples were collected at three time points: before the first vaccination (time I), one month after the first vaccination (time II), and one month after the second vaccination (time III), to quantify sex hormone levels (i.e., testosterone and estradiol) and the production of antibodies in response to the hepatitis B vaccinations.

Results Women's immune response (i.e., the production of hepatitis B antibodies) was negatively associated with testosterone levels one month after the first vaccination and positively associated with estradiol levels one month after the second vaccination. A decrease in testosterone levels between time II and time III was also observed. No differences in estradiol levels over time were found.

Conclusion Our results demonstrate negative associations between testosterone and immune responses in women as previously described for males of several animal species, including humans. There were also positive associations between estradiol and immune responses, highlighting the immunomodulatory role of sex hormones in women. Potential bidirectional effects between immune markers and sex hormones are discussed.